How Low Outdoor Temperatures Affect Your Heat Pump’s Performance

“How efficient will this heat pump be when it’s freezing cold in February?”

Most homeowners only pay attention to the rated temperature of a machine. By rated amount of heat I mean if it’s a 12,000 BTU machine it will continue to produce 12,000 BTU’s of heat even at low temps. However, the rated temperature doesn’t tell the story of how efficient that heat pump will be in the depths of winter.

To fully understand what I mean, you first must understand how a heat pump works. Heat pumps don’t actually create heat; they move it.

Does a Heat Pump Generate or Move Heat?

Air to air heat pumps, which is what most Nova Scotians are installing (ductless and ducted systems) do not generate heat like an oil furnace or electric resistance baseboard heater. Instead, they move heat from one place to another using a refrigeration loop.

Here’s the basic process:

The outdoor unit of your heat pump pulls air over a refrigeration coil with a large fan.

Heat in the outdoor air is absorbed into this refrigerant coil.

The amount of heat that is absorbed at low temperatures varies based on the type of refrigerant and efficiency of the machine

That refrigerant line runs into your home and the indoor heat pump unit

Another fan blows air over the refrigerant coil of the indoor unit, extracting heat in the process, and pushing it out into your living space.

That’s the simple version of how a heat pump works. Yes, there is a compressor and some other valves the refrigerant goes through, but at it’s most basic operation that is what a heat pump does.

The chemical makeup of today’s heat pump refrigerants (currently R410A) is such that it does not freeze until an extremely low temperature. So even though it is freezing to us outside, there is still a heat differential between the outdoor air temperature and the freezing point of the refrigerant. It’s because of this differential that heat can be absorbed into the system.

How Outdoor Temperature Affects Heat Pumps Effectiveness

As the outdoor temperature gets colder, there is less and less heat in the air for the refrigeration system inside a heat pump to extract. It then becomes the job of the compressor and other components to amplify the heat in the system.

No matter what heat pump you have, as it gets colder out its ability to extract heat and move it inside is reduced. However, not all heat pumps abilities degrade at the same rate.

Most machines will operate just fine down to about -5°C or so. It’s down below this temperature that you will notice your heat pump not being able to keep your living space a comfortable temperature. You may need to turn on your backup heating source.

Sizing and Efficiency are Most Important

It’s down below the -5°C to -8°C that having a properly sized and efficient machine becomes extremely important.

An efficient machine such as Daikin’s LV or High Capacity units will effectively produce their rated amount of heat down to about -20°C. Where a less efficient machine may have dropped off to 7,000 – 8,000 BTU’s of heat at this cold temp.

KEY TAKEAWAY: By rated amount of heat I mean if it’s a 12,000 BTU machine it will continue to produce 12,000 BTU’s of heat even at low temps.

What does this mean for you as the homeowner? If you have the less efficient unit, it could mean having to turn on your electric or oil heat to stay comfortable.

Moral of the story

Don’t buy a less expensive heat pump thinking you got a deal. You don’t have the full cost of operating any heat pump until a year later, and you have experienced the full heating system with that machine.

A unit with a quality compressor, valves and other parts runs efficiently. Meaning it won’t work as hard (read cost as much) to maintain a comfortable level of heat in your space. So you won’t have to turn on your secondary heat as often.

For more information on Daikin’s high-efficiency model heat pumps and to receive a risk-free estimate contact us at South Shore HVAC today. Give us a call at 902-530-5002 or submit the form on this page to request an estimate. We service from Chester to Shelburne.